Creating the Door Placer for a Room

[Koldar]

This task was written by @micheledusi . Your task is to create a class that works with the RoomGenerator (see Issue #3 ) in order to substitute some "plainWallTiles" with "RoomWallTiles".
These tiles are prefabs used to visualize the 3D model of a room; they all have the same "modular" dimension, so you can switch from one to another without moving adjacent tiles.
The RoomGenerator instantiates a room with no door. To complete this task your "DoorPlacer" has to take off some of those walls and put some "door pieces" instead. The door pieces, in the alpha version, have to be instantiated only at ground floor.
To decide how and where to put a door, you methods should accept some door coordinates: a possibility is to create a struct "CardinalDoorPlacement" which is composed by the cardinal orientation of the wall (north, south, west, east), and the number of the tile to substitute.
When you can substitute every tile subset with a new door tile set, your task is accomplished.